Because LCDs have the advantages of portability, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, etc.
A conventional LCD typically includes a liquid crystal panel, a backlight module with a plurality of light sources for illuminating the LCD panel, and a backlight modulation circuit for modulating illumination provided by the backlight module.
Referring to FIG. 6, one embodiment of an analog method for modulating illumination provided by a backlight module of an LCD is shown. In the method of FIG. 6, as a voltage level for a driving voltage increases, the illumination provided by the backlight module also increases. Likewise, as a voltage level for a driving voltage decreases, the illumination provided by the backlight module also decreases. The one-to-one correspondence between the voltage and the illumination under the control of the backlight modulation circuit may modulate the backlight module in a range of 70% to 100% of a maximum illumination for the backlight module.
In a digital method for modulating illumination provided by a backlight module, pulse width modulation (PWM) and pulse frequency modulation (PFM), may be used. FIG. 7 illustrates one embodiment of a PWM method for modulating illumination provided by a backlight module. In the PWM method, a duty ratio of a pulse voltage signal is changed in order to modulate the illumination provided by the backlight module. When the duty ratio increases, the illumination provided by the backlight module also increases. Similarly, when the duty ratio decreases, the illumination provided by the backlight module also decreases. Accordingly, the illumination provided by the backlight module can be modulated via changing the duty ratio of the pulse voltage signal. Using the PWM method, the illumination provided by the backlight module can be modulated in a range from 30% to 100% of a maximum illumination for the backlight module.
One drawback of the above-described analog and digital PWM methods is that they can only modulate the illumination provided by the backlight module either in a large and imprecise range or in a small and precise range. However, if an LCD needs to be modulated in a large and precise range, then many modulation commands and signals may need to be analyzed. Accordingly, modulating the many commands and signals wastes valuable processor cycles and consumes additional energy.
It is desired to provide a new backlight modulation circuit and a method for modulating illumination of a light source which can overcome the above-described deficiencies.